KA-0036Rate, time, distance
4 points, difficulty 2 of 3Level 5–6about 75sRavi cycles 12 km at 24 km per hour, then walks 6 km at 4 km per hour. How many minutes does the whole journey take?
Hints
Take them one at a time. The first gives nothing away.
1A nudge
Work out each leg on its own.
2The strategy
Time is distance divided by speed, so do the two legs separately and add the times. Convert both to minutes before adding so nothing is left in mixed units.
3The full solution
Cycling: 12 divided by 24 is half an hour, which is 30 minutes. Walking: 6 divided by 4 is one and a half hours, which is 90 minutes. Together that is 120 minutes.
Solution— no shortcut on this one
Do each leg separately. Cycling 12 km at 24 km/h takes 12 divided by 24 = 0.5 hours, or 30 minutes. Walking 6 km at 4 km/h takes 6 divided by 4 = 1.5 hours, or 90 minutes. The whole journey is 30 + 90 = 120 minutes. The transferable idea: add times, never average speeds, and convert to one unit before adding.
Why this is on the test: Journeys in two legs test whether a student computes each leg separately and keeps the units consistent while adding.